Andrew Millard's Publication Abstracts 1992-1996

An argument for the possibility of uranium uptake by buried bone
taking place through the adsorption of uranyl species on bone mineral is
advanced. In the light of this a diffusion-adsorption model for uranium
uptake by buried bone is developed, the necessary constants are
evaluated from the literature and from laboratory measurements of the
partition coefficient between solution and bone mineral. The geochemical
and hydrological parameters which control uptake are discussed. The
predictions of the model are shown to be in general accordance with the
timescale, magnitude, and distribution of uranium uptake in
archaeological bone. Using the model, specific predictions of the
variation of apparent uranium-series ages in bone can be made, and bone
is shown clearly not to conform to the closed system assumption. When
the model is extended to tooth enamel it is found to be incompatible
with the early uptake model used for ESR dating, but to fall between the
early uptake and linear uptake models. Similarly, it suggests that
uranium-series dates on enamel assuming a closed system are liable to
underestimate the true age by at least one-third.

Millard AR, and Hedges REM (1995) The role of the environment in uranium uptake
by buried bone. Journal of Archaeological Science 22:239-250.

Previous studies by a number of workers have shown that uranium is
inhomogeneously distributed in excavated bones. It has been suggested
that the higher concentrations of uranium found towards the outside of
some bones may indicate that the uranium has been taken up by a
diffusion process. This paper briefly outlines a quantitative model of
uranium uptake by diffusion and chemical reaction, and the measurement
of uranium distributions in a number of samples. The relationship of
these distributions to environmental factors and to other diagenetic
changes is explored, and comparisons made between them and the model.
Finally the implications of these results for the uranium series dating
of bones are considered, and the way forward in modelling uranium uptake
suggested.

This paper develops a theory for describing those diagenetic changes
in bone which involve its interaction with groundwater. Three main
processes are considered, as examples of such changes; namely the uptake
of uranium, the dissolution of bone, and the increase of crystallinity
of the bone mineral (carbonate hydroxyapatite or dahllite). Here simple
models of the chemistry involved are postulated (although how bone
interacts with water on a molecular scale is not clearly known) in order
to demonstrate the theory with explicit mechanisms and values. Greater
emphasis is given to uranium uptake, since the model used is
comparatively detailed, being based on the authors' previous work.

The basic assumption is that the rate-limiting process in diagenetic
change is the movement of solutes to, from, or how the physical
structure of the bone itself, together with the hydrology of the burial
site, interact to determine how water and its solutes move into, within
and from a bone during burial. This interaction can be of three kinds,
defined by the site hydrology. These are termed here, diffusion,
hydraulic flow and recharge. All three types may operate together, and
their relative importance depends on the extent to which the pore
structure of a bone has been altered by diagenesis, as well as the type
of chemical change taking place. It is shown that diffusion is usually
the most common and important process, but that it is possible to
predict the hydrological regimes in which other mechanisms dominate. It
is shown how knowledge of site hydrology (mainly the specification of
soil structure and moisture variation), the physical state of the bone,
and the chemistry of the diagenetic observation, suggesting this
approach to be on the right lines. Qualitative predictions also result
from the theory. The main value of this approach is to identify those
situations where particular diagenetic changes are simplest (e.g. sites
where the hydrology gives rise to a single and quantifiable hydraulic
process) so that they may be decisively tested against the quantitative
predictions of the theory.

Four diagenetic parameters have been chosen to represent the state of
diagenesis of bone buried on archaeological sites. They are:
histological preservation, protein content, crystallinity, and porosity.
How these parameters are measured is described and results from
populations of bones from three different sites are presented. The
results show the extent and variation in the degree of change, both
within a site and between sites. In particular the correlations between
diagenetic parameters are examined, which give clues about the processes
which cause alteration. The value of porosity determinations (both at
the intercrystalline level, and at coarser levels) in revealing the
degree of diagenetic change in bone, and in underlying the dynamics of
the interaction between buried bone and the surrounding water is
stressed. The data also indicate (but are too restricted to prove) the
following: Microbiological attack is generally complete within less than
500 years; Substantial levels of protein may remain in bone after
maximal micromorphological alteration; Loss of protein appears to be
independent of other diagenetic change; The correlated loss of
microporosity with increase of crystallinity suggests these changes may
arise from the dissolution, perhaps with subsequent recrystallization,
of the smallest hydroxyapatite crystallites.

Blair J, and Millard A (1992) An Anglo-Saxon landmark rediscovered: the stanford/stanbricge
of the Ducklington and Witney charters. Oxoniensia 57:342-348.

Notes the rediscovery of a paved causeway crossing a stream, the only
previous evidence for its existence being AS writings. There is
discussion of the documentary and archaeological evidence, providing
insight into AS use of the terms `ford' and `bridge'.